The brain is composed of neurons and other cell types in connected networks that process sensory input, generate motor commands, and control other behavioral and cognitive functions. Neurons communicate primarily through electrochemical pulses that transmit signals between connected cells within and between brain areas. Stimulation technologies that affect electric fields and electrochemical signaling in neurons can modulate the pattern of neural activity and cause altered behavior, cognitive states, perception, and motor output.
Electrical stimulation applied to the head and neck area, such as transcranial electric stimulation (TES) through scalp electrodes, has been used to affect brain function in the form of transcranial alternating current stimulation (tACS), transcranial direct current stimulation (tDCS), and transcranial random noise stimulation (tRNS). Relative to tDCS, tACS and tRNS offer the advantage of reductions in pain, tingling, and other side effects on the scalp. Another strategy to reduce side effects is to use a high-density-tDCS (HD-tDCS) system with smaller electrode pads, such as ones sold by Soterix Medical. tACS also has the advantage of being inherently temporal in nature and thus capable of affecting, inducing, or destructively interfering with endogenous brain rhythms.
TES is advantageous for modulating brain activity and cognitive function in man. TES has been shown to improve motor control and motor learning, improve memory consolidation during slow-wave sleep, regulate decision-making and risk assessment, affect sensory perception, and cause movements. Systems and methods for TES have been disclosed (see for example, U.S. Pat. No. 4,646,744 to Capel; U.S. Pat. No. 5,540,736 to Haimovich et al.; U.S. Pat. No. 8,190,248 to Besio et al.; U.S. Pat. No. 8,239,030 to Hagedorn and Thompson; U.S. Patent Application Publication No. 2011/0144716 to Bikson et al.; and U.S. Patent Application Publication No. 2009/0177243 to Lebedev et al.). Many such TES systems described in the prior art require surgical implantation of components for electrical stimulation on the head of a user (see for example U.S. Pat. No. 8,121,695 to Gilner and U.S. Pat. No. 8,150,537 to Tanaka and Nakanishi). Although tDCS systems with numerous electrodes and a high level of configurability have been disclosed (see, for example, U.S. Patent Application Publication Nos. 2012/0209346, 2012/0265261, and 2012/0245653 to Bikson et al.), as have portable TES systems for auto-stimulation (U.S. Patent Application Publication No. 2011/0288610 to Brocke), such prior art TES systems are complicated, and would be difficult for an end-user (e.g., a patient or subject wearing the device) to apply and operate.
The simplest form of TES is tDCS. Several open source tDCS projects have released designs for inexpensive TES systems, including the ‘Thinking Cap’ from Grindhouse Wetware and the Go Flow. In such examples, the electronic circuitry requires a voltage supply (generally 9 V or 12 V); a current regulator to supply constant current as the impedance between an electrode and a subject's head changes slightly (e.g. due to movement, sweating, etc.); and some circuitry to ensure that spikes of current do not pass into the subject. Additional components can be added to select the current delivered, limit the time of stimulation, and provide visual or other indicators of stimulation.
tACS requires additional hardware to deliver alternating currents to the electrodes at an appropriate frequency. An oscillator, microcontroller, or timing circuit can be used to deliver a desired time-varying stimulation. In some designs, a digital-to-analog converter is used.
tRNS additionally requires a microcontroller or other processor configured to provide random values with appropriate structure that are then converted to an analog signal and used to gate current at a the desired intensity (e.g. at a desired amplitude, frequency, and/or duration) through appropriate circuitry.
For each form of TES, one or more pairs of electrodes coupled to a subject's head or body are used to deliver the desired energy to the subject's brain or nervous system. A battery or AC power supply is used to supply power. For example, hardware and software systems for TES typically include: a battery or power supply safely isolated from mains power by magnetic, optic, or other techniques; control hardware and/or software for triggering a TES event and controlling the waveform, duration, intensity, and other parameters of stimulation of each electrode; and one or more pairs of electrodes with gel, saline, or another material for electrical coupling to the scalp. Such prior art apparatuses are typically cumbersome, and can be heavy and difficult to operate and apply.
Historically, stimulation electrodes used in TES have been relatively large, on the order of about more than 2 cm by 2 cm. The motivation for large electrode pads has been to reduce the tingling, itchy, or painful sensation created at the edge of the electrodes from the generated electric field. For instance, Feurra and colleagues used a 3 cm×4 cm electrode and a 5 cm×7 cm electrode for stimulating somatosensory cortex (Feurra et al., 2011a). Bikson and coinventors have proposed a ‘high density’ electrode system with multiple smaller electrodes arranged in groups and improved coupling of the electrical fields to the scalp in order to reduce discomfort (U.S. patent application Ser. No. 12/937,950, titled “Apparatus and Method for Neurocranial Electrostimulation” by inventors Marom Bikson, Abhishek Datta, Fortunato Battaglia, Maged Elwassif).
Similarly, Schutter (Schutter and Hortensius, 2011) used conductive-rubber electrodes placed in wet sponges saturated with Parker Spectra 360 electrode gel (Parker Laboratories, Fairfield, USA). Other skin surface mounted electrodes known to be employed in TES include adhesive stimulation electrodes that maintain positioning by adhering to the scalp. In other embodiments, a band, helmet, or other head-mounted assembly maintains the positioning of the stimulation electrodes. In general, these prior art systems all include electrodes that may be attached to the subject and are connected, typically by a wire or other connector, to a base unit that is remotely located from the electrodes and the subject's head. These base units may include the stimulator/controller for applying the waveforms.
Various commercial and custom systems for triggering a specified stimulus waveform using one or more pairs of TES electrodes have been described and are well known to one skilled in the art of brain recording or TES, e.g. DS2 or DS3 Isolated Stimulator (Digitimer Ltd., Welwyn Garden City, Hertfordshire, U.K.). Such systems are not typically portable or wearable, at least in part because of subject safety concerns; in order to provide sufficient power (current, voltage) to a subject to produce an effect, many systems require bulky and durable signal conditioning and electrical isolation, and therefore physically isolate these control units from the subject (and particularly the subject's head).
Described herein are apparatuses (devices, systems, etc.) that may provide effective stimulation (e.g., TES) to produce a cognitive effect in a subject, yet be intuitive and easy to apply and operate and may be lightweight, durable and self-contained, so that the entire apparatus (electrodes and stimulator) can be applied and worn on the subject's (patient's) head. Some or all of the control functions for the apparatus may be remotely controlled, e.g., using non-transient control logic executable on a remote processing device (e.g., smartphone, pad, computer, etc.). The apparatuses and methods of making and using them, described herein may address many of the shortcomings and may dramatically improve upon prior art TES apparatuses and methods.
Also described herein are exemplary brain stimulation techniques that are known in the art can also be combined with (and improved upon by) TES to create advantageous forms of neuromodulation. For example, transcranial ultrasound neuromodulation employs ultrasound for stimulating neural tissue rather than for imaging, see, for example, U.S. Patent Application Publication No. 2011/0178441 and International Patent Application No. PCT/US2010/055527 (Publication No. WO 2011/057028). Such parallel or additional techniques may include transcranial magnetic stimulation, optogenetic stimulation, and electrocorticography.
Transcranial magnetic stimulation (TMS) induces electric fields in the brain by generating a strong (generally pulsed) magnetic field with a coiled electromagnet at or near the head. The magnetic field is transmitted painlessly and efficiently through the skin and skull to the underlying neural tissue. Deep brain stimulation (DBS) requires implantation of electrodes targeted to a brain area of interest, generally one at some depth from the brain surface. A long thin electrode assembly, generally with several conductive leads near the tip delivers electrical stimulation to a tissue of interest. DBS is an effective strategy for treating Parkinson's disease in subjects unresponsive to drugs.
Optogenetic stimulation uses light of a specified wavelength to activate an engineered protein expressed in neurons or other cell types that modifies the electrical and/or biochemical activity of a targeted cell. For deep brain applications, light is generally introduced via an implanted optical fiber.
Electrocorticography (ECoG) arrays are electrodes implanted on the surface of the brain or dura. ECoG arrays can be used to record electrical potentials and/or stimulate underlying cortical tissue, for instance to map the focal point of a seizure.